Nutating type torque transmitting systems are well known for their utility as speed reduction mechanisms. Typically in these systems, an input member is provided with means for initiating nutating movement on the part of an intermediary idler member. To obtain a speed reduction, the nutating member is normally held rotationally stationary with respect to a stator, while the intermediate member engages an output via gear teeth, rotating the same at a speed determined by the relative numbers of teeth on the idler and the output.
Of the nutating devices known in the prior art, all have employed teeth as a mechanism by which torque is transmitted. Applicant has found that nutating mechanisms of this sort are disadvantageous, owing to the extreme precision which must often be observed in manufacturing the gear faces in the member initiating the nutation. If such mechanisms are of conventional gearing material, substantial expense is entailed in machining the gears to acceptable tolerances. Further, since precision is at a premium, it is often difficult to form the gears out of extrudable materials such as plastic.
Conventional nutating gear mechanisms also are incapable of transmitting large torque loadings, as 100 percent of the torque is transmitted at any given time by only a small percentage of the total number of gear teeth. This is an inherent problem in prior art nutating mechanisms, due to the fact that the wobbling intermediate member could not be in contact with more than a few teeth of the stator and/or the output member at any given time. This distinct disadvantage is overcome in the present invention by means of a unique departure from the use of gear elements as the mechanism by which torque is transmitted. In particular, the stator, idler, and output member are formed with surfaces which constitute raceways for two or more series of rolling elements provided in the form of tapered roller bearings. Owing to the novel curvature of the respective members and the relationship between coacting grooves, the rollers are maintained in contact with both the driving and driven surfaces at all times, while they rollingly transmit torque between the respective members.
All known prior art nutating mechanisms have employed coacting teeth as at least part of the torque transmitting means. The only known example of a prior art system which does not exclusively employ teeth for this purpose is disclosed in the patent to Vallance, U.S. Pat. No. 1,748,907. This patent discloses a speed reduction mechanism in the form of a nutating gear system, wherein an input shaft initiates wobbling motion of an intermediate member 7, via the engagement of a portion 9b of the intermediate member with an angled or canted portion of the input shaft 2. Radially outwardly on the member 7 are disposed a train of teeth 10 which engage stator teeth 11 formed on a portion of the stationary housing 5. Inside of the cup-member 7 are arranged a number of hemispherical recesses 7b, in which are fixedly seated a like number of balls 8. These balls are in turn in engagement with a continuous curved groove 6b formed in an output member 6. As with other known nutating systems, the engagement between stator teeth 10, 11 prevents the intermediate member 7 from rotating during nutation, so that output rotation is effected solely by means of the engagement between the fixed balls and the groove. As the idler member 7 nutates, the balls 8 will successively cam the element 6 rotationally by engaging the walls of the curved groove.
Although being of interest for the feature noted above, the patent to Vallance nonetheless suffers from the several deficiencies noted previously. In particular, torque transmission via the system is limited by the small number of teeth engaged at the stator, and strict manufacturing tolerances must still be observed both in the manufacture of the teeth and the groove itself. In any event, the teachings of Vallance by no means approach the present system, wherein at least one series of rollers rollingly transmit torque between respective elements of the device.
Other prior art nutating mechanisms employing rolling elements in some capacity are disclosed in U.S. Pat. Nos. 3,139,772, 2,913,911, 3,525,890, and 3,094,880. In these patents, the rolling elements are normally used in connection with the means initiating motion on the part of an intermediate member, which is provided with the usual teeth.